This invention relates generally to transmission of television signals and more particularly to systems therefor using the correlation between frames to save the volume of information to be transmitted.
One of such television transmission systems previously known in the art is that proposed by J. C. Candy et al. in the article entitled "Transmitting Television as Clusters of Frame-to-Frame Differences", The Bell System Technical Journal, Vol. 50, No. 6, July - August, 1971, pp. 1889-1917. In that system, picture elements are each compared between successive frames and, when the magnitude of the frame-to-frame difference is greater than a predetermined threshold value, it is regarded as significant.
A considerable saving of data to be transmitted can be obtained by transmitting only those elements having a significant frame-to-frame difference but, in order to obtain a further saving, the techniques of ignoring significant changes in the picture that are isolated and coalescing runs of significantly changed elements that are separated by a small number of unchanged elements into a so-called "cluster" are employed. The technique of ignoring isolated changes is effective to obtain savings in the volume of bits required to signal changes of amplitude of picture elements and their addresses. The technique of coalescing runs or the so-called "bridging" technique further saves the volume of address data to be transmitted as runs of changed elements interrupted by three or less unchanged elements are transmitted in a continuous fashion as a cluster or bridged run. This techniques, however, naturally involves a disadvantage that the number of picture elements transmitted is unnecessarily increased because of the bridging element or elements included in the cluster which are insignificant in nature.